Attempts have been made to provide flame spray apparatus which include an internal burner operating to produce an ultra-high velocity flame jet. One such ultra-high velocity flame jet apparatus is set forth in my earlier U.S. Pat. No. 2,990,653 entitled "Method and Apparatus for Impacting a Stream of High Velocity Against the Surface to be Treated" issuing July 4, 1961. Such apparatus comprises an air cooled double or triple wall cylindrical internal burner whose interior cavity forms a cylindrical combustion chamber. Downstream of the point of initial combustion, the chamber is closed off by a reduced diameter flame jet nozzle.
In a further attempt to provide such ultra-high velocity flame spraying apparatus for metal, refractory material or the like, introduced to the high velocity flame spray stream in powder form or in solid small diameter rod form, an arrangement was devised involving the utilization of a hot gaseous primary jet stream of relatively low momentum which fuses and projects a stream of molten particles into a second gaseous jet stream of lower temperature, but possessing a very high momentum. Such type of apparatus and method is set forth in my copending U.S. patent application Ser. No. 152,966 filed May 23, 1980, and entitled "Method and Apparatus for Ultra High Velocity Dual Stream Metal Flame Spraying", now U.S. Pat. No. 4,370,538 which issued Jan. 25, 1983. The method and apparatus of my more recent application employs the first stream in the form of an oxy-fuel flame or an electric arc-producing plasma, while the second stream comprises a flame-jet produced by an air/fuel flame reacting at high pressure in an internal burner device. In combining the two streams, preferably the molten particles are carried by the first stream at relatively low velocity but relatively high temperature, while the supersonic jet stream which impinges the entrained molten particles against the surface to be coated at ultra high velocity is discharged from an internal burner combustion chamber wherein combustion is effected at relatively high pressure. The second stream is directed through an annular nozzle surrounding the primary stream. Further, the primary and secondary streams are projected through a nozzle strcture to the point of impact against the substrate to be coated by the liquid particles travelling at supersonic speed, under the acceleration provided by the secondary jet of heated gas.